Impact of pulsating flows on particle deposition in forward osmosis with spacers

Fouling continues to be a limiting factor in membrane processes. Pulsating feed flows have the potential to decrease fouling while maintaining a constant pressure drop over the module. This study quantifies the impact of pulsating flows on particle deposition in a forward osmosis system with spacers at a mean crossflow velocity of 14 cm s⁻¹ and permeate water flux of 18 L m⁻² h⁻¹. Carboxylate modified polystyrene beads were tracked by fluorescence microscopy in situ and real-time during the first 4 h of deposition with feed flow pulsations up to a frequency of 10 Hz, while experiments were conducted with a constant crossflow velocity as a reference. Imaging at 30 s intervals revealed deposition rates of up to 2.6 times higher at steady state, as compared to flow pulsations of 10 Hz. Consequentially, average deposition was reduced by a factor of 3.5 from steady state (109 ± 67 beads mm⁻²) to pulsating feed flow (31 ± 17 beads mm⁻²) after 4 h of deposition. The results of this research provide new fundamental insights related to the constraints and advantages of using pulsating flows for fouling mitigation in forward osmosis systems.